Despite widespread implementation of legal prevention strategies, the epidemic of HIV infection among IDUs persists unabated. Consequently, illegal and highly controversial needle/syringe exchanges (NSEs) continue operations in cities across the United States. Currently there is growing interest among national and local policy makers in information concerning these clandestine AIDS interventions. We intend to conduct an ethnographic process evaluation of Prevention Point, an NSE located in San Francisco. Our research objectives are to produce a thorough understanding of the ways in which NSE is currently implemented, utilized and experienced. Data collection will consist of both ethnographic field observations, depth interviews and closed-ended questions. Field observations will be conducted at all five Prevention Point sites. Depth interviews will be conducted with four subsamples: 50 primary exchangers (IDUs who exchange at program sites); 50 secondary exchangers (IDUs who exchange needles/syringes through primary exchangers); 50 non-exchangers (IDUs who do not exchange); and 25 Prevention Point staff. We will explore the factors which serve as barriers to, or facilitate participation in, NSEs. We plan to not only study formal activities and anticipated outcomes. Finally, we will provide a detailed description of the impact of this intervention on HIV drug and sex-related risk behaviors.